1. Field
An apparatus and method for controlling a linear compressor are disclosed herein.
2. Background
Generally, compressors are devices that converts mechanical energy into compression energy of a compressible fluid. A compressor may be used as a part of a freezing device, for example, a refrigerator, or an air conditioner.
The compressors are categorized into reciprocating compressors, rotary compressors, and scroll compressors. In the reciprocating compressors, a compression space, into and from which an operating gas, such as a refrigerant, is sucked and discharged, is provided between a piston and a cylinder, and the piston performs a rectilinear reciprocating motion in the cylinder to compress the refrigerant. In the rotary compressors, a compression space, into and from which an operating gas, such as a refrigerant, is sucked and discharged, is provided between a cylinder and a roller that eccentrically rotates, and the roller eccentrically rotates along an inner wall of the cylinder to compress the refrigerant. In the scroll compressors, a compression space, into and from which an operating gas, such as a refrigerant, is sucked and discharged, is provided between an orbiting scroll and a fixed scroll, and the orbiting scroll rotates along the fixed scroll to compress the refrigerant.
The reciprocating compressors linearly reciprocate the piston in the cylinder to suck, compress, and discharge a refrigerant gas. The reciprocating compressors are categorized into a reciprocating method and a linear method depending on a method of driving the piston.
The reciprocating method is a method that couples a crankshaft to a motor which is rotated and couples a piston to the crankshaft, thereby converting a rotating motion of the motor into a rectilinear reciprocating motion. On the other hand, the linear method is a method that couples a piston to a movable element of a motor performing a rectilinear motion to reciprocate the piston using the rectilinear motion of the motor.
The reciprocating compressors each include an electric unit or device, which generates a drive force, and a compression unit or device that receives the drive force from the electric device to compress a fluid. A motor is generally used as the electric device. In the linear method, a linear motor is used as the electric device.
As the linear motor directly generates a rectilinear drive force, the linear motor does not need a mechanical conversion device, and a structure of the linear motor is not complicated. Also, the linear motor reduces the incidence of loss caused by energy conversion, and as the linear motor does not include a connection part that causes friction and abrasion, the linear motor generates less noise in comparison to other motors. Further, when a linear reciprocating compressor (hereinafter referred to as a “linear compressor”) is applied to a refrigerator or an air conditioner, a compression ratio is changed by changing a stroke voltage applied to the linear compressor, and thus, the linear compressor may be applied to variable control of a freezing capacity.
In the reciprocating compressors, in particular, the linear compressors, the piston performs a reciprocating motion in a state in which the piston is not mechanically restrained in the cylinder, and thus, when an excessive voltage is suddenly applied to the linear compressor, the piston is dashed against a wall of the cylinder, or compression cannot be normally performed because the piston cannot travel due to a large load. Therefore, a control device for controlling a motion of the piston when a load or a voltage is changed is essential.
Generally, a compressor control device detects a voltage and a current applied to a compressor motor and estimates a stroke to perform feedback control using a sensorless method. In this case, the compressor control device includes a triac or an inverter as a means for controlling a compressor.
In the compressor control device, control based on a compressor motor should be performed. In the related art, the compressor control device performs control using a method that measures a motor constant for each model of motor to directly input the measured motor constant to a control program, and detects a voltage and a current to estimate a stroke using the sensorless method, thereby performing feedback control.
However, such a method undergoes an inconvenient process of previously measuring a motor constant to directly input the measured motor constant to a control program. Also, when a control target of a control device is changed due to repair, inspection, or breakdown, a compressor is controlled by repeating the inconvenient process.
Alternatively, control is performed using a method in which a control program defined for each model of motor is built into a device. However, using the defined control program, a kind of controllable motor is limited, and whenever a control target is changed, the control program is changed. Also, a number of control programs should be built into a device so as to control various kinds of motors, and for this reason, compatibility of a control device is largely limited.